Help me understand bottleneck COAL

[ghbucky]

OK, so loading handguns, COAL is pretty easy to manage, since the brass on straight walled cartridges doesn't really expand (at least in my exprience).

But, Rifle brass does expand. So, if I'm looking at load data what is the brass length that COAL is based on?

I'm looking at the spec for 5.56 and it says the case length should be 44.7 mm. My once fired, sized brass is measuring 44.71, but my Lee trimming tool looks like the brass would need to be about 2mm longer before it would bite.

Where did I go into the weeds?

 

[nhyrum]

With bottle neck brass you have a(time to) trim length, they just call it trim length, but that's when you need to trim, and a trim to length. The length of when you trim, what you trim to. There's usually 10 thousands between the two. If your book only has one number, trim length, that's the length you cut to, and you can wait till it's 10 thou past that to trim.

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[ghbucky]

What I was missing was trim to length

Couple of youtube vids help set me straight.

Lee's instruction video shows a guy finger tightening the pilot into the chuck and proceeding to trim. I had to grab a wrench to tighten the pilot rod in far enough to get me to 1.75" trimmed length.

 

[ghbucky]

Thanks

 

[308Loader]

COAL = Cartrage-OverAll-Length, completed cartrage tip to tail. sometimes refered to as COL.

Trim length is what is refered to above. Trim to length for 223/556 is 1.750. triming is usually done after sizeing. 1.760 is max length of the sized brass before it needs to be trimmed.

 

[Unclenick]

Actually, COAL is Cartridge Over-all length. Up until the 1950's "overall" and "over-all" had two different meanings, the former meaning "taken altogether", as in, "he had a good life, overall", and the latter referring to the total physical length of something, as in, "the skiff was nine feet, over-all". By 1960, the hyphenated spelling had been dropped from Webster's, and "overall" became the spelling for both meanings, with the context determining which was meant.

"Over-all" formally has the initials O.A., while "overall" has just the initial "O". Hence, C.O.A.L. is the set of initials for an obsolete form of spelling, while C.O.L. is consistent with modern spelling.

 

[ghbucky]

OK, so I'm not worried about terminology.

What I'm trying to ask is:
If the case length can be variable, then how do I determine what my COAL, or COL or whatever should be?

Now I understand that I have 1/1000 variability, but I'm only looking for 1/100th precisioin.

 

[308Loader]

I would say if the empty sized case is 1.760"+ in length it needs to be trimmed (so sayith SAMMI). If it is under the max trim length (1.760-) I might leave it alone. I have a habbit of triming all sized 223/556 brass to min (1.750) in large batches. consistancy is key, especally if you crimp your bullet. Once you trim, it may be a while before you need to trim again, dependent on how you size, and other varibles.

I might be wrong but what i think your asking is more related to trim length. maybe COAL and seeting depth?

 

[Old_School]

OK, so I'm not worried about terminology.

What I'm trying to ask is:
If the case length can be variable, then how do I determine what my COAL, or COL or whatever should be?

Now I understand that I have 1/1000 variability, but I'm only looking for 1/100th precisioin.

It doesn't matter what brass length is...COAL is inclusive of brass length. i.e. it's measured from the tip of the bullet to the casehead.

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[308Loader]

delete, I might disageree.OAL-COAL might include a brass case that is too longfor chamber, or over crimp a bullet.

 

[44 AMP]

COL (COAL) if you're being archaic, is CARTRIDGE overall length.

Lyman uses the term "loaded length with bullet" in their old manuals.

It means total length of the loaded round from the base of the case to the tip of the bullet.

Case length is a different measurement, it is the measurement of the length of the EMPTY case.

 

[ghbucky]

I might be wrong but what i think your asking is more related to trim length. maybe COAL and seeting depth?

I'm apparently doing this wrong.

Let me start over.

If I have a fired, sized brass that is between 1.75 and 1.76 inches, and I have a load recipe that specifies a min COL of 2.2 inches based on the specific bullet, then if I seat the bullet to a 2.2in COL I know I have a specific volume behind the bullet per the recipe.

So, what is the length of the case that the recipe expects to use to reach that 2.2? Is it the 1.75 trim to length, or the SAAMI max length of 1.76?

If I'm approaching max load data, is that .01 inch difference enough to be a problem?

Sorry if I'm garbling this badly. I'm a handgun loader who just sized and trimmed a rifle case for the first time ever and boy am I getting a new education.

 

[sako2]

measure a case without a bullet in it. That measurement should be no longer than 1.760 if it is trim it to 1.750. The 2.2 measurement is with a bullet in the case. that measurement is taken from the case head to the tip of the bullet.

 

[pwc]

If your brass (case) is correctly trimmed to the length you want for your rifle, then it is the bullet shape and seating depth that determines COAL.

 

[nhyrum]

Ah, yes.COALl is CARTRIDGE overall length. The overall length of a loaded round.

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[308Loader]

"If I have a fired, sized brass that is between 1.75 and 1.76 inches"

Spec says 1.760 max, mouth to head is max brass length. Trim down to 1.750 for min. Anywhere in between should be safe for random rifle.

 

[ghbucky]

Yes, OAL is with a bullet seated. I stipulate this is the case

What I'm getting at:
If the recipe says 2.2" OAL, and it assumes my brass is 1.76" long, and I trim to 1.75" and seat the bullet to a 2.2" OAL, I have now reduced the volume behind the bullet beyond what the recipe specified, potentially raising the pressure beyond the never exceed limit.

Am I right here?

 

[sako2]

No. If you go shorter than 2.2 then you reduce the volume.

 

[Old_School]

Yes, OAL is with a bullet seated. I stipulate this is the case

What I'm getting at:
If the recipe says 2.2" OAL, and it assumes my brass is 1.76" long, and I trim to 1.75" and seat the bullet to a 2.2" OAL, I have now reduced the volume behind the bullet beyond what the recipe specified, potentially raising the pressure beyond the never exceed limit.

Am I right here?

You're over-thinking it. As long as you don't exceed max brass length, you're good.

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[nhyrum]

Yes, OAL is with a bullet seated. I stipulate this is the case

What I'm getting at:
If the recipe says 2.2" OAL, and it assumes my brass is 1.76" long, and I trim to 1.75" and seat the bullet to a 2.2" OAL, I have now reduced the volume behind the bullet beyond what the recipe specified, potentially raising the pressure beyond the never exceed limit.

Am I right here?

No. The overall length of the loaded round is the same, regardless of length. The capacity, measured from the bottom of the case, to the bottom of the bullet, doesn't change. No change in cbto measurement, nothing. You aren't measuring from the case mouth to bullet tip, that's literally the only thing that changes. Nothing else (ok, brass/total weight change too)

Think about it this way. 9mm Luger case length is . 754. Let's say we load a particular bullet to 1.125. now, let's imagine we somehow grew a piece of brass, to an extreme, to an oal of one inch. Same load. Bullet seated to an oal of 1.125(don't ask me how. It's a perfectly spherical chicken in a total vacuum type situation) the powder capacity, which is from the bottom of the inside of the case, to the bottom of the bullet, stays exactly the same.

Make sense...? To anyone?

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